Birth defects affect approximately 5% of all infants in the USA, three-fourths involving the head, face, and oral tissues. The most frequent craniofacial birth defects are orofacial clefts: cleft lip +/- cleft palate (CL/P) affects ~1 per 1100 births in the USA, and cleft palate ~1 per 1600 births. Orofacial clefts thus represent a considerable public health problem and expense, and most cases cannot now be predicted or prevented. Isolated, "non-syndromic" CL/P (nsCL/P) is the most common craniofacial birth defect, accounting for approximately 70% of all cases of CL/P. nsCL/P is a non-Mendelian, multifactorial disorder, due to multiple genes, each exerting a relatively small effect, interacting with each other and with environmental factors to ultimately result in defective action of specific pathways and genetic networks during fetal craniofacial development. However, few of the genes, and none of the environmental influences, that contribute to nsCL/P are currently known with certainty. The goal of this proposal is to identify the genes, pathways, and genetic networks that are involved in craniofacial development and that thus represent potential targets for genetic and non-genetic determinants of nsCL/P. Identification of these targets will be necessary to devise therapeutic strategies ultimately aimed at preventing this debilitating and disfiguring birth defect. It is currently very difficult to accurately study gene action during craniofacial development in the human. Accordingly, we plan a careful microarray study of gene expression profiles in the developing face of the mouse, in which genetic background (C57BL/6J), careful timing of fetal age, sampling at numerous timepoints, and analyses of many replicate samples can all be readily achieved. In addition, we plan an analogous study of facial development in mice homozygous for a null knockout allele of the Ski locus, carried on the C57BL/6J background. These Ski -/- mice have an exceedingly high rate of midline facial clefts, providing an invaluable comparison of gene expression during aberrant craniofacial development that, in particular, should identify genetic pathways and networks of the developing facies that are responsive to Ski. For genes that appear of particular importance during facial development, we will identify and validate human SNPs for use in future linkage and association studies of nsCL/P. We will apply state-of-art bioinformatics tools to analyze and interpret the data, all of which we will deposit in appropriate public data repositories.